I have been able to use line breaks successfully with radio buttons, but I'm getting some commas when I try the code with a text area. Here's one that still has a comma:
<input type="hidden" name="product[15]"><textarea cols="30" rows="1" name="product[15]"></textarea>
<input type="hidden" name="product[30]" value="{br} ," />

A comma is placed after every entry. A comma cancels out a comma. You will need to play with it using different options. You can try putting the break and/ comma before a field. Or after or both. Sometimes it can take time to figure out what will work with all of your possiblities. Trial and error is what I do.

One thing to consider is do you REALLY want the info broke apart into so many lines in the cart? It looks nice but If someone wants to purchase multiple stockings The cart might run out of space.